This invention relates to an apparatus for efficiently effecting the sterilization and volume-reduction treatments of infectious medical wastes such as a used hemodialyzer, a used syringe, a used syringe needle, a used gauze and a used container.
In order to prevent the secondary infection caused by infectious medical wastes discharged from hospitals, dialysis facilities and the like, the Japanese Welfare Ministry announced, on Nov. 7, 1989, the guidelines on methods of treating such wastes, and these regulations have been put into force from Apr. 1, 1990. Therefore, in principle, the hospitals, the dialysis facilities and the like have the obligation to sterilize the infectious medical wastes in their facilities.
It has been thought that, for example, steam, a band heater, hot air circulation, and a high-frequency generator could be used for heating and sterilizing the infectious medical wastes.
Referring to the prior art, Japanese Patent Unexamined Publication No. 1-176486 discloses a treatment method and a treatment apparatus in which used syringes of a synthetic resin and used syringe needles are put into a heat-resistant vessel, and these wastes are heated to a predetermined temperature and melted by an electric heater or heaters and a far infrared heater or heaters, thereby sterilizing them, and then the molten wastes are cooled and solidified.
Japanese Utility Model Unexamined Publication No. 1-144040 discloses an apparatus for heating and sterilizing wastes in which the wastes are heated and sterilized by hot air, and then the wastes are crushed and reduced in volume by a crusher.
Japanese Patent Publication No. 51-25470 discloses an apparatus for treating plastic wastes in which the plastic wastes received within a cylinder are heated by heaters contained in a bottom plate and a piston, and are melted mainly at the surfaces of these wastes simultaneously with the compression of the wastes, to thereby mold them into an integral block.
Japanese Patent Unexamined Publication No. 1-315383 discloses an apparatus in which used disposable syringes are heated and sterilized by an electric heater or heaters and a far infrared heater or heaters mounted on a side wall or walls and/or a bottom wall of a heating furnace. Also, this publication discloses, as one embodiment, a method in which wastes to be treated are melted in a heat-resistant vessel, and then are cooled and solidified into an integral block containing needles, and thereafter this integral block is taken out.
Japanese Patent Unexamined Publication No. 1-263410 discloses an apparatus in which wastes are heated by microwaves to be dried and burnt into ashes.
Problems with the steam heating are the production of waste water and a legal limitation on a pressure vessel. The heating by the band heater or the like causes a local overheating which adversely affects a heat transfer efficiency. As regards the heating by the hot air circulation, a satisfactory heat transfer is not obtained merely by blowing a blast of hot air, which may cause local overheating. The high-frequency heating has a problem in that particularly after the evaporation of water, a local overheating may occur because of the difference in selectivity of the high-frequency absorption by the materials.
Relatively small medical wastes, such as a syringe, can be sufficiently treated by hot air circulation or the band heater, and also the high-frequency heating can be effectively used for incinerating medical wastes. However, for treating large-size medical wastes, such as a hemodialysis instrument which is composed mainly of plastic materials containing polyvinyl chloride, and contains a large amount of water therein, these treatment means have both merits and demerits, and are not suitable. When the medical waste containing polyvinyl chloride is incinerated or subjected to a local overheating, there is a possibility that poisonous gas such as hydrogen chloride may be produced.
Particularly when a large-size hemodialyzer, composed of several kinds of plastic materials of different melting points, is treated by the use of the treatment method and apparatus disclosed in the above Japanese Patent Unexamined Publication No. 1-176486, many portions of the hemodialyzer remain unmelted depending on the treatment temperature, and therefore the volume reduction (molding) is inadequate. Also, the large-size waste, such as a hemodialyzer, is liable to undergo a local overheating because of the use of the electric heater and the far infrared heater, and therefore there is a possibility that poisonous gas, such as hydrogen chloride gas, may be produced from polyvinyl chloride.
In the crushing method performed by the crusher in the apparatus for heating and sterilizing wastes, disclosed in the above Japanese Utility Model Unexamined Publication No. 1-144040, the volume reduction effect is not always satisfactory, and besides the maintenance of the cutter of the crusher is necessary, and also noises and vibrations are large, and many power sources are needed.
In the apparatus for treating plastic wastes, disclosed in the above Japanese Patent Publication No. 51-25470, sterilization is not intended at all, and the concept disclosed in this publication is to coat only the surface of the wastes with the molten material, and therefore there is a disadvantage that the stability of the molded block is unsatisfactory.
When a large-size waste, such as a used hemodialyzer containing water therein, is treated by the apparatus disclosed in the above Japanese Patent Unexamined Publication No. 1-315383, the temperature of the waste can not rise easily only by hot air circulation, and the sterilization is not satisfactory, and the treatment time is long. In addition, since the hemodialyzer is composed of a plurality of kinds of plastic materials, some of these plastic materials become molten while the others do not become molten, depending on the treatment temperature, so that the volume reduction can not be effected adequately.
When a waste such as a used hemodialyzer, or a waste comprising various tubes of different plastic materials, is treated by the apparatus disclosed in the above Japanese Patent Unexamined Publication No. 1-263410, a large amount of poisonous gas such as hydrogen chloride is produced. Therefore, consideration must be given to the material of the apparatus, and besides an exhaust gas treatment device of a large volume is needed for dealing with the exhaust gas. This complicates the construction of the treatment apparatus, and increases the size thereof. Further, in the method in which the ashing is carried out by microwaves so as to effect the volume reduction, much electric power is required, and the apparatus itself is heated to elevated temperatures, and therefore this apparatus can not suitably be installed in a hospital or a clinic.
In the conventional treatment apparatus using microwaves, since the microwaves are applied to the whole of the heating chamber, much of the microwave energy is wasted, and therefore the efficiencies of the heating, sterilization and volume reduction of the waste to be treated are not good. In addition to these disadvantages, there exists another problem that a door of the heating chamber is complicated in construction in order to prevent the leakage of the microwaves from the apparatus and also to maintain the airtightness of the heating chamber.
The infectious medical wastes contain a plurality of kinds of plastic materials. For example, when the material ratio of one set of waste dialysis instruments, including a hemodialyzer, a blood circuit (including tubes and etc.), a syringe and a physiological salt solution vessel, was analyzed, the following results were obtained:
______________________________________ (1) Polyvinyl chloride 50 wt. % (2) Polystyrene or polycarbonate 30 wt. % (3) Cellulose or synthetic membrane 5 wt. % (4) Polyethylene, or polypropylene, or silicone 5 wt. % (5) Polyurethane and stainless steel 10 wt. % ______________________________________
Incidentally, the natures of the main plastic materials among the above materials are shown in Table 1 below.
TABLE 1 ______________________________________ Soften- Kind of Melting ing material point point Notes ______________________________________ Polyvinyl about 65 to HCl gas is produced at chloride 170.degree. C. 85.degree. C. above 190.degree. C. Poly- about 90 to Deformation temperature: styrene 230.degree. C. 102.degree. C. 70 to 100.degree. C. (ASTM D648) Softening point: 97 to 100.degree. C. (ASTM D1525 - 58T) Polycarbo- about 145 to Deformation temperature nate 230 to 165.degree. C. (ASTM D648) 260.degree. C. 130 to 136.degree. C. (18.6 kg/cm.sup.2) 136 to 142.degree. C. (4.6 kg/cm.sup.2) (medium- about Softening temperature: density) 120.degree. C. about 100 to 120.degree. C. (ASTM Poly- D1525) ethylene Deformation temperature: 50 to 66.degree. C. (ASTM D648) Polypro- about 96 to pylene 170.degree. C. 105.degree. C. (ASTM D1525) ______________________________________ Remarks: ASTM (American Society of Testing Material)